Method and system of high-speed servicing using multi-terminal network with serial data transfer

TECHNICAL FIELD OF THE INVENTION

The present invention relates to data transmission networks and, in particular, to a method and system for providing high speed services using a multi-drop serial data transmission network. The present invention involves the time division multiplexing mode supporting data (AMD, TDM), such as a plurality of audio broadcasts, and stereo communication, in particular using the adapted network EIA-485 or RS-422.

BACKGROUND

Minutes EIA-485 (formerly «RS-485") is a standard protocol for serial data transmission hardware for multi-site networks that can be connected to the control devices 32 and 32 receivers to one (two-wire) bus. The maximum data rate of 10 megabits per second for a distance of 1.2 m or 100 kilobits per second for a distance of 1200 m.

Currently, some companies-manufacturers produce EIA-485 transceivers with the function of making pre-emphasis and de-emphasis function of the corresponding receiver, which allows to double the transmission distance by using data rates of magnitude higher than 400 kilobits per second. These devices can be used to increase the data rate by a predetermined distance (up to 35 Mbps for distances less than 10 m) and allow to connect up to 128 transceivers.

EIA-485 protocol is one of the most used multi-drop communication protocols and one of the most economic physical layer protocols. Many electronic devices equipped with EIA-485 ports. This protocol is also widely used in the on-board electronic systems of vehicles.

Of interest are the following documents: «Electrical characteristics of Generators and Receivers for Use in Balanced Digital Multipoint Systems (ANSI / TIA / EIA-485-A-98) (R2003)», «Comparing Bus Solutions, Application Report SLLA067 - March 2000", Texas Instruments, http://polimage.polito.it/-lavagno/esd/bus.pdf.

SUMMARY OF THE INVENTION

The aim of the invention is to provide a method and system for providing the transmission of digital information over multiple communication channels using multi-drop serial bus, such as EIA-485 bus.

Another object of the invention to provide a method and a system allowing to reduce the bandwidth required for the provision of multicast service via a serial bus.

Another object of the invention to provide a method and system that allows high-speed service at distances exceeding the standard distance, for example between the cars of the train.

Another object of the invention is to provide a method and a system allowing to reduce the number of buses required and related equipment.

Another object of the invention to provide a method and a system allowing to renounce the use of more expensive multicast protocols, multicast information.

Another object of the invention is to provide a method and system using a very simple method of synchronizing the encoder, decoder and a possible repeater.

Another object of the invention is to provide a system that requires very small amount to accommodate the hardware devices and cable connections.

In accordance with one aspect of the present invention, a system for broadcasting multi-channel signals to a receiving station over a two-wire bus and includes:

an encoder having:

a multiplexer for multiplexing digital data corresponding to the signal channels and to generate an information stream;

Framing unit coupled to the multiplexer and for separating the flow of information on data frames and to insert the header frame comprising at least a specified sequence;

transceiver pre-emphasis coupled with the block framing encoder and allowing connection to two-wire bus;

a receiver with de-emphasis which can be connected to the two-wire bus, and comprising:

a decoder that can be connected to the receiving station and comprising a conversion unit frames for reproducing digital data corresponding to the multichannel signal, based on the data frames, said converting unit frame is configured to use the previous data frame in the registration error for the current data frame ;

a timing circuit comprising a phase lock loop based on the sequence for sampling the incoming information stream using said predetermined sequence and to restore the system timing signals, and

selector channels connected to the conversion unit personnel and for controlling the multi-channel signals reproduced conversion unit frames.

In accordance with another aspect of the invention provides a method of providing high speed broadcast services by means of a serial multidrop network data comprises:

time multiplexing of high-speed data services to generate the flow of information;

transforming the information stream into information frames, a header and a parity bit, wherein the header has a size of less than 32 bits;

transmitting data frames with pre-emphasis on the multi-drop serial data network;

receiving data frames from the de-emphasis of the multi-drop serial data network;

converting the synchronized data frames in a pre-selected high speed data services.

BRIEF DESCRIPTION OF DRAWINGS

Detailed description of preferred embodiments of the invention given below with reference to the following drawings.

1 is a diagram of a network architecture with continuous data transfer destined for an entertainment audio system integrated in the seat, in accordance with the present invention.

Figure 2 is a diagram of an audio encoder in accordance with the present invention.

3 is a diagram of an audio decoder in accordance with the present invention.

4 is a diagram of a data relay according to the present invention.

5 shows a diagram of the format of an information frame in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

1 shows a system with continuous transmission of data to the broadcast of stereo audio and multi-channel communication with high quality to individual passenger seats of the public vehicle by means of a multi-drop communication network 16, also referred to as two-wire bus. The system comprises an audio encoder 2, an audio decoder 4 and the repeater 6 data. The encoder 2 performs (if necessary) an analog-digital conversion (ADC, ADC) signals and generates data frames. One channel of the RS-485 interface allows the simultaneous transmission with up to five to ten non-compacted or compressed stereo. 4, the audio decoder may be integrated in the arm rest (not shown) of the user. Additional decoders 4 may be connected to the network 16 for servicing more hours Isla passengers, each passenger may choose the audio channel to listen for entertainment purposes. Repeater 6 provides for data recovery, filtration and re-transmitting signals to RS-485 multi-drop network of another segment of serial data, for example, if necessary, to the next carriage structure (not shown).

The same system can be used for providing other services such as access to the Internet, the user appliance control and other purposes and in different situations, in particular in the passenger plane, on cruise ships, in-store the CD / DVD, etc. . Repeater 6 is used only if necessary.

The proposed system uses a combination of a plurality of devices connected by an original manner. The delta-sigma analog-to-digital converters 8 (ADC) 10 and digital to analog converters (DACs) are used to perform analog-to-digital conversion and vice versa. Transducers of this type provide oversampling frequency modulation and a closed-loop, which allows the sharing of forming high-quality digital signals.

Delta-sigma AD converter differs from the AD converter of another type, because it produces a sampling of the input signal with a frequency markedly higher than the maximum input frequency. The traditional inverters, do not use the principle of oversampling, for example AC converters successive approximation, perform a full conversion of only one sample of the input signal. Another unique property of the delta-sigma converter is used with a closed modulator circuit (not shown). The modulator is not only continuously integrates the error that occurs between the result approximate the ADC and the input signal, but also reduces the noise. This combination of oversampling and closed-loop modulation provides a very powerful technology.

Delta-sigma concept can also be used in the CA-converter. The main difference between sigma-delta D and D converter is the repetition frequency of the output signals. The ADC block is used for the decimation conversion of high frequency pulses having a small resolution in the low frequency words with a higher resolution. Delta-sigma DACs, with the other hand, performs the inverse operation. In this case, the interpolation operation allows sampling to produce digital output signals at a higher frequency. There was thus obtained output signals having a high resolution / frequency and allows a simple low pass filtering to produce an output analog signal.

Another technique uses transceivers EIA-485 12 with pre-emphasis 12 and corresponding receiver having a function 14, de-emphasis, which increases the distance and speed reliable data transmission over the bus 16 by reducing the level of intersymbol interference (ISI, ICP), resulting in long cables.

To reduce the total cost of a built-in seat audio entertainment can be modified to use an extended bus EIA-485 as a line of digital data transmission between the encoder and the decoder 2 4. Bus EIA-485 has three major advantages: it is a bus, provides a multi-drop data transmission is very economical to use. The problem is the need to transmit five (5) unconsolidated quality digital stereo sound channel with bandwidth limited at 10 megabits per second. Only audio transmission requires bandwidth 7.056 megabits per second. It should be noted that an increase in the data rate increases the likelihood of errors.

Network 16 permits the transmission of digital audio data transmission of up to five (5) and stereo audio streams (stream 10 in phase 2), including the streaming data. Adding predistorter allows increasing a data rate with a large number of loads.

EIA-485 protocol is a protocol of the physical layer. Bus EIA-485 allows the use of different formats of data packets at the data level. The protocol uses mostly simple commands Asko (ASCII, American Standard Code for Information Interchange). Typically, the minimum value of the service data is 32 bits (4 bytes), which in many cases is not optimal. In accordance with the present invention, a limit of 16 bits of overhead data.

There broadcasting multichannel device E1 / T1. Device E1 support a data rate 2 megabits per second, and the devices T1 respectively support a data rate of 1.5 megabits per second, whereas improved EIA-485 devices support up to 35 megabits per second. Thus, at the same sample rate and the level of quality (44.1 kHz for high-quality stereo) solution E1 / T1 would support a smaller number of channels. Furthermore, the technology of E1 / T1 is a point to point solution. To adapt this technology to the multi-drop network conditions requires the use of additional devices, which leads to complication and increased cost.

The multiplexer 18 serves to perform time multiplexing of data (HDR) communication channel during transmission over EIA-485 bus 16. The same multiplexing principle may be applied to other communication protocols such as RS-422 protocol, providing service to other species.

In a possible embodiment unconsolidated audio data generated by the analog-digital converter 8, are of 16 bits per channel and each channel is performed with the data sampling frequency 43.17 kHz.

Thus, according to the invention form several data channels multiplexed in the format of one of AMD EIA-485 bus. The system provides the broadcast signals over a plurality of communication channels (e.g. formed by multiple audio servers 44) to one or more receiving stations 102 (e.g., audio listening stations) over a two-wire bus 16, such as EIA-485 bus. The encoder 2 of the system has a multiplexer 18 which serves to multiplex the digital data corresponding to the signals of communication channels (e.g., signals generated by audio servers 44) and producing a flow of information. Framing unit 104 is coupled to multiplexer 18 and serves to separate the flow of information on data frames 32 (see. Figure 5). Transceiver 12 with the function of making the predistortion unit coupled to the framing 104 of the encoder 2 and can be connected to the two-wire bus 16. A receiver 14 with predistortion correction function may be connected to a two-wire bus 16. The decoder 4 is connected to receiver system 14 and may be connected to the host station 102. The decoder 4 is provided with a conversion circuit 106 frames / sync designed to recover digital data corresponding to the signals previously selected channels, based on the data frames 32, and to synchronize the conversion block with respect to the frame data frames 32 and the selection circuit communication channels 66 (see Fig. 3) connected to the frame conversion unit 106 and provides a choice of signals from a variety of communication channels to restore the frame conversion unit 106.

Encoder 2 is a delta-sigma analog-to-digital converters 8 for converting the plurality of channel signals into digital form for the multiplexer 18. Likewise, the decoder 4 has the delta-sigma digital to analog converter 10 coupled to the frame conversion unit 106 for converting the digital data corresponding to signals selected from a plurality of communication channels to analog form for the receiving station 102. In the case where the signals of the plurality of communication channels are already presented in digital form may be an exception in the encoder 8 converters 2. Further, in the case of using a receiving station 102 may be a digital input exception transducers 10 from the decoder 4.

High service mode broadcast in multicast network serial data can be performed by the system by time-multiplexing the data of high-speed services for forming information flow, forming on the basis of the information flow data frames 32 with a header 20 having a size less than 32 bits, and the bit 22 checks parity, transmit data frames 32 as amended by pre-emphasis on the multi-drop network 16 serial data transmission, reception information frame 32 with de-emphasis of the multicast network 16 serial data transfer, recognition given sequence of bits in the received data frame 32, synchronization received data frames 32 using the internal synchronization signal and external synchronization signal extracted from the data frames 32, after the phase comparison is executed after recognizing a predetermined sequence of bits, and converting the synchronized data frames 32 in a pre-selected high speed data services.

5 shows a data frame structure and communication protocol serving to multiplex signals 24 AMD transmission of these signals over EIA-485 bus with a header 20 together minimum size data 22 and error correction. In accordance with the present invention can, for example, reduce the amount of overhead EIA-485 to 18 bits using a format without a seal, which is less than any of the commercial applications. Each unconsolidated stereo connection includes 32 bits. Five separate channels discredited with frequency 43.17 kHz may be multiplexed in the HDR format and transmitted on a single EIA-485 bus. The bandwidth required for transmission of five (5) unconsolidated stereo channels is:

((5 × 2 channels (stereo) × 16 bits), 17 bits (the header) +

1 bit (parity)) × 43,17 kHz = 7.6843 Mbps.

The bandwidth required for transmission of the ten (10) compressed (16 to 10) stereo channels is:

((10 × 2 channels (stereo) × 10 bits) is 11 bits (the header) +

1 bit (parity)) × 43,17 kHz = 9.152 megabits per second.

In fact, one EIA-485 bus can simultaneously support up to six channels of unconsolidated (ten multiplexed channels), because the total bandwidth is not greater than 10 megabits per second. Nevertheless, it is always useful to use as little as possible of the communication channel as approaching the boundary indicator 10 megabits per second increases the probability of errors.

To perform the synchronization header size used is preferably 17 bits (11 bits in the case of data compression), and preferably comprise 22 bit parity. As a result, we can reduce the overhead for the optimal use of the bandwidth as compared to conventional systems having a minimum value of 32 bits of overhead data.

As shown in Figure 1, the synchronization of the encoder 2, the decoder 4 and the repeater 6 may be provided using a quartz oscillator 26, 28, 30 (see FIG. 2, 3 and 4) used in each of these devices, wherein Sync does not require additional configuration. The synchronization procedure may be performed by the phase synchronization of the local clock signal and the external timing signal extracted from the incoming information stream. Operation phase comparison may be set so as to be performed every time after, for example, detection of at least four sequentially transmitted bits with a high level of information in the header 20 of the frame 32 for providing a constant threshold for the phase comparison. After this phase synchronization is performed on admission of the next sequence of four bits. Header 20 comprises at least four sequentially transmitted bit with a high level to guarantee a phase comparison operation at least once for every message or frame 32.

It may also be provided by management errors in the audio service, which allows the end user to eliminate audible distortion audio signal in the event of failure. In each network there is a possibility of distortion of transmitted data. To manage such potential problems using 22-bit parity, which allows to check the integrity of data received. Parity bit is an element of each data frame 32, for example, of 178 bits. It is enough to guarantee the maintenance of high-quality audio options. When an error occurs, the analyzer 34 (see Fig. 3) is not able to select the position of incorrect data; In this case, an error handling strategy consisting in the retransmission of the preceding audio data. A similar strategy is used for the detection of loss of data frames or violation of phase synchronization. Two recent events should be excluded.

It is possible to use a logarithmic data compression to increase the number of data channels transmitted over the same line EIA-485. Logarithmic encoder / decoder 36, 38 can be used for most of the available levels for weak signals. This process can be considered as a seal for the signal amplitude. The use of this technique makes it possible to transmit up to 10 stereo audio and one data line EIA-485.

The function of the network repeater 6 may seem very simple, but this module has a fairly complex structure. The repeater uses the same technology that is used in the audio decoder 4 for data tracking but in this case the emphasis is on high tracking precision instead to reduce the response time tracking. The objectives of the relay is to reduce the level of phase fluctuations, the compensation of the phase shifts and the preservation of the integrity of the data.

Task decrease the phase fluctuations in the network 16 is achieved by using circuit 40 analog and / or digital phase synchronization. Phase shifts of signals generally associated with the influence of intersymbol interference (ICP). SMEs are due to multiple effects of signal degradation in the network. One of the effects associated with signal attenuation and dispersion of the frequency components in the propagation of the signal in the transmission line. Another effect related to the change of duration leading and trailing edges of signals due to changes in the sequence of logical ones and zeros is called the "effect of the phase offset determined by a logical sequence." As a result of the impact of these effects on the information pulse decreases its amplitude, time shift occurs, there is a flattening of the fronts and "naplyvanie" pulse on the adjacent time segments or unit intervals. Phase synchronization with the phase of the repeater 6 of specially formed pure sample the pulse allows the rest of the audio data stream based on this phase, which contributes to a marked weakening of the level of phase fluctuations.

To reduce the cost of the entire system may be unaddressed signaling between cars in the broadcast mode. At the level of the decoder it is possible to use a simple, but very effective procedure for re-modeling errors. The objective is to form a repeater without error signals with weak phase fluctuations for regular wagon composition.

Shared power supply 42 provides supply voltage for all components of the system. Secondary supply voltage formed by galvanic isolation, can be chosen at 12 V. Each device is preferably provided with individually isolated power supply. The primary power supply can use standard voltage. Each component of the system is equipped with the advanced serial port EIA-485 (not shown). To reduce ground leakage and maintain the voltage in the corresponding standard range preferably provides galvanic isolation of all communication interfaces.

Encoder 2 provides five digitizing analog stereo channels generated audio servers 44. To maintain a high level of signal quality using delta-sigma converters 8. Analog interface between audio servers 44 and delta-sigma converter 8 can be arranged through the amplifiers 46 and low-pass filters 48 . amplifiers 46 provide level adjustment signal conversion and lowpass filters 48 serve to reduce the potential distortions occurring due to aliasing. Vehicle seal unit 50 (LUT, look-up table), and TS demultiplexer unit 108 (see FIG. 1) may be used if necessary.

One purpose of the invention is to provide a transmission opportunity five unconsolidated quality digital stereo sound channel bandwidth limited at 10 megabits per second. Actually, for the transmission of the audio signal requires bandwidth 6.907 megabits per second. By increasing the data rate increases the number of errors and increases the level of phase fluctuations. The number of service data is reduced by using the header 20 comprising 17 bits, and one parity bit 22 (see. Figure 5). When in the information sequence corresponding to the header 20, the signal in the current channel audio transmission may be replaced by a zero signal, provided that the decoder 4 has the ability to correctly interpret such information.

The structure of the header 20 provides immunity to various problems. Title 20 is transmitted in a time shorter than the transmission of audio data to generate quality indicator diagram at the link. Using a single parity bit 22 based on one frame of the audio data 32 can effectively detect errors in each frame 32.

Formation of the audio data stream with a predetermined transmission rate requires the use of different frequency components. In practice, the ratio between the speed of the output bits and the reference frequency is 0.6953125 (89/128). This ratio is obtained by dividing the amount of overhead added to the data, based on the number of transmission channels on a sampling frequency used by converters 8 oversampling. To generate such a frequency can be used phase synchronization circuit having a programmable divider circuit 52 (N) feedback and one output (M) which serves to form the respective frequency components. The frequency component is generated: Fout = Fref * N / M. Another programmable divider 54 serves for dividing the frequency 11.052 MHz crystal oscillator 26 for eight (8) to obtain a signal with a frequency of 1.3815 MHz is used by shift registers 56, while synchronizing converters 59 parallel to serial, and the analyzer and controller 58 bit stream separating the flow of information in the data frames, is performed by means of the divider 52.

There may be a way to suppress all the digital audio channels. Suppression command 60 may come from an external device (not shown). One possible use of this procedure involves the continuation of the previous data transmission over the period of the team's 60 suppression.

Check the audio system is quite difficult to perform using real data. The audio data is usually complicated, so tracking the data transmission process in the system is a complex task. To facilitate inspection of the entire system can use the sequence generator (not shown) in one of the audio servers 44. In this case, instead of selecting the samples from the ADC converter 8 obtained from some given sequence generator sequence.

3 shows a block diagram of the audio decoder 4 is the most critical components of the system. Although this device has a complicated structure, it remains relatively low. The decoder 4 allows you to maintain the high quality parameters of audio signals even in difficult conditions due. The entire system is designed so that it provides high-quality sound without the feedback from the encoder 2. The decoder 4 is synchronized with the incoming flow of information, highlights stereo channels, check for possible damage to the data and performs its function. As a result, even in the occurrence of signal distortion listener can not hear other sounds.

Fundamental frequency is set equal to the encoder 2 and the decoder 4. Even when using these devices in both the quantity of quartz oscillators frequency differences do not exceed a few ppm. In this case, the strategy involves sampling data with a frequency greater than 8 times the input data rate, and control the phase relationship with the internal reference signal. The algorithm allows small phase changes in the reference signal. Over time, these changes may be unacceptable and initiate execution phase adjustment procedure. It can be seen that from the sampling block 62 to the voltage controlled crystal oscillator (UNKG, VCXO) 28 provides feedback 64. Even though the generator 28 is made on the basis of the quartz oscillator, its frequency can be varied in the range of ± 100 ppm . When using this method it is possible to eliminate the accumulation phase shift as frequency reference will always be synchronized to the incoming flow of information. Comparing the phases may be performed each time after the registration of at least four sequentially transmitted bits high levels in the header 20, thus maintaining a constant threshold for the phase comparator (in the sample stage 62). Then, for the next phase of the synchronized sequence of four bits (a sequence header is a component).

3A architecture does not allow to trace the execution order of operations on data demultiplexer. This optional feature can be based on the following simple principle: an inverse logarithmic function can be encoded and placed in a dedicated memory unit 38 (see FIG. 1). This function is an inverse logarithmic function, recorded in the memory unit 36 ​​of the encoder 2. With the use of these functions can be given a signal good dynamic characteristics with minimum distortion.

The user interface 66 may be limited to four push buttons 68 serving for channel selection and volume control. Each switch button 68 enables exclusion effect debounce via circuits 70 exceptions bounce and appropriate commands, for example commands to increase / decrease of 72 channel number and the increase / decrease 74 volume level is supplied to the corresponding block, in particular to the analyzer 34 and amplifier 76 with adjustable gain. Volume control can be performed using the digital potentiometer logarithmic type, equipped with individual meters 76 and 80 shift register, receiving the appropriate data from the serial port. For channel communication apparatus controls the entire operation, wherein the analyzer 34 is installed in a simple counter for each communication channel.

In each network there is a likelihood of data corruption. To avoid this potential problem in the system provided for the use of 22-bit parity (see para. 5), which allows to check the integrity of data transmitted. This bit is part of each data frame 32 of 178 bits, which should be sufficient to maintain a reliable audio quality. When an error occurs, the analyzer 34 is not able to select the position of the incorrect data. Error handling strategy involves reusing the preceding audio data. Thus, the frame conversion unit 106 allows the use of the prior data frame 32 in identifying error information for the current frame. A similar strategy is used in failure detection function data frames or in violation of phase synchronization. The last two situations must be exceptional.

In the configuration of the network continuously transmitting digital audio signals assumes a 2 audio encoder, serving up to several hundred audio decoders 4. This requires the use of high performance design that provides the ability to conduct a quick check of health personnel of the manufacturer. The design of the decoder involves the transfer of management functions by an external intelligent device (not shown). This device must be configured to send the team up / down link, and increase / decrease the volume level and check for indicators of harmonic distortion audio connection, and reliability indices. Such a device can also solve the problem of validating the operation interface 66 push buttons. All production tests may be conducted using a three-wire interface data, synchronization signals, the load.

Audio decoder 4 does not require any settings. The only installation in conditions associated with the installation, if necessary, the plume contact the RS-485.

The decoder 4 decodes the incoming data frames using decoders 82 convert the serial to parallel, and shift registers 84 under control of the analyzer 34. The low pass filter 86 may be used to filter the selected audio channel before amplification.

4 shows a diagram of the data repeater 6, which uses the same technology developed for the audio decoder 4 allows tracking data, but in this case the emphasis is to achieve a high tracking accuracy rather than to ensure a quick response in the tracking process. Repeater task is to reduce the phase fluctuation compensation of phase shifts and maintaining data integrity.

As noted above, the strategy for phase tracking is similar to the strategy used by the decoder 4, the audio data, and the block 92 the sampling phase locked to input data via a feedback loop comprising a comparator 94 phase-analog converter (DAC) 90, a voltage controlled crystal oscillator 30, a programmable frequency divider 98 and the reference circuit 96. The essential difference between the decoder 6 and the repeater 4 is to its greater accuracy. Instead of sampling input data with a frequency greater than 8 times the input data rate, they operate with a sampling frequency of 16 greater. Moreover, instead of the feedback loop with three different conditions (+100 ppm, 0 ppm, -100 ppm) for the voltage controlled crystal oscillator (UNKG) 30 is added with 88 feedback control 16 levels. The comparison operation may be performed once for a data frame, and the phase can be synchronized to the rest of the information flow. Switching phase may be initiated upon detection of a specific sequence in the header 20. Header 20 reduces the effects of electrical noise in the cable connection.

The data lines are exposed to high-intensity electrical pulses or pulsed radiation. To reduce the distortions introduced by the data on the level at the repeater provides digital filtering of the input data using a digital filter 100. The filtering may be accomplished by repeatedly sampling the input data during their working time and of correlation analysis between samples.

The present invention solves several problems of the prior art. The invention makes it possible to create a system through data that can transmit digital data of a plurality of communication channels on a single EIA-485 bus. This reduces the bandwidth required to transmit the service data on the EIA-485 bus. It also allows you to deploy high-speed service at great distances. The proposed approach can reduce the number of required buses and related hardware devices. This approach also eliminates the need for a more expensive multicast protocols, multicast data. We propose a very simple principle of synchronization between the encoder, decoder and a transponder. Also provided is a method of correcting corrupted data. Proposed to use a logarithmic data compression to further increase the number of channels supported in a single EIA-485 bus. The system requires very little space to accommodate the hardware devices and cable connections. Space saving is a significant advantage when using the system in vehicles.

The present invention determines the communication protocols at the physical layer and the communication protocols for the levels located above the physical layer, and can transmit digital data signals on the basis of the time division multiplexing (AMD) via bus EIA-485 at speeds up to 10 megabits per second over distances exceeding 150 m.

It should be understood that various changes and modifications may be made to the above embodiments without departing from the spirit of the invention. For example, the decoder 4 may be used two delta-sigma digital to analog converter 10 is connected to the conversion unit frame (formed by the circuit 34, 82, 84) for converting the digital data corresponding to two independently selected signals from a plurality of communication channels for the transmission in two stations 102. Thus a single receiver 14 can be connected to multiple decoders 4.